Activity-Based Aptamers as Bioimaging Tools for Probing Organics, Inorganics, and Enzymes. PROJECT SUMMARY / ABSTRACT Aptamers are functional oligonucleotides that bind a specific target (ligand), which is typically a small organic molecule. Some in vitro-selected RNA aptamers can bind and substantially increase the fluorescence quantum yield of fluorogenic ligands that are otherwise poorly fluorescent in their unbound state. Consequently, there is considerable interest in developing methods in which aptamers can be used for fluorescence imaging of molecules in living cells. Expansion of these methods as practical and adaptable platforms could lead to advanced detection strategies for biomarkers associated with human diseases. However, the limitations lie in that each RNA aptamer is only capable of recognizing a defined, characteristic structure of organic molecules. Here we describe (Aim 1) an application of designer small molecules to enable a single RNA aptamer to detect multiple as well as structurally diverse disease- associated biomarkers, including inorganic molecules and enzymes; we term this activity-based aptamer (ABA) system. In addition, we will (Aim 2) expand the translational potential of RNA aptamers by proposing a chip design that introduces reusability into ABA systems. We will microarray solid surfaces with nanoneedles and nanostraws for capture-assisted detection of specimens. These proof-of-principle studies will lay the foundation for developing novel molecular tools to further investigate cellular dysfunction and lead to point-of-care application.